U.S. Pat. No. 5,655,401 discloses a forming tool that serves to reduce the cross section of connecting webs by means of which sheet metal parts produced by punching a metal sheet are connected to a skeleton surrounding the sheet metal parts. The connecting webs, also called “micro-joints”, create a temporary connection between the sheet metal parts and the skeleton and ensure that, during and after the punching operation on the metal sheet, the produced sheet metal parts and the skeleton can be handled as a unit. To avoid that the connecting webs break under the effect of the stresses occurring while handling of the sheet metal parts and of the skeleton together, the connecting webs have to be dimensioned adequately. At the same time, it must be possible, after the joint handling of the sheet metal parts and of the skeleton, to release the sheet metal parts from the skeleton with minimal effort. To this end, the cross section of the connecting webs between the sheet metal parts and the skeleton is reduced by means of known forming tools.
The known forming tools include a forming punch with a beveled punch tip and a forming die with a planar support surface and a die recess sunk into the planar support surface. The forming punch is assigned to the one side of a connecting web to be processed and the forming die to the other side. With a processing stroke performed along a stroke axis, the forming punch is moved towards the forming die. In doing so, the forming punch acts upon the connecting web arranged between the forming punch and the forming die with the beveled punch tip. Due to the impact by the punch tip, the connecting web is squeezed and the thickness of the connecting web between the forming punch and the forming die thereby reduced, and, furthermore, the connecting web is bent over an edge that is formed on the forming die by the support surface and a surface that laterally delimits the die recess and extends parallel to the stroke axis.
As a result, a fracture zone is created on the connecting web where the cross section is reduced relative to the remainder of the connecting web. If all connecting webs between the sheet metal parts of the processed metal sheet and the skeleton surrounding the sheet metal parts are pressure formed in the described manner, just shaking the unit comprising the sheet metal parts and the skeleton is sufficient to break the connecting webs at the fracture zones, thereby detaching the sheet metal parts from the skeleton. In doing so, a burr that projects beyond the surface of the sheet metal parts is left and has to be removed mechanically.